An address block is a routed range of IP addresses allocated together on the internet, often as a contiguous chunk managed by a provider, network operator, or enterprise. In IPv4, this is commonly described as a CIDR block such as /24 or /16; in IPv6, blocks are much larger but serve the same purpose.
Address blocks matter in cyber security because they help identify whether traffic comes from many truly independent networks or from a smaller set of shared infrastructure. Attackers may spread requests across multiple blocks to make scraping, credential attacks, or scanning look geographically diverse and harder to block with simple IP bans. Defenders use address-block analysis to spot reuse, cluster related sources, and distinguish normal user traffic from coordinated automation. A large number of IPs spread across many blocks can suggest a broad footprint, but repeated behavior across those blocks may still reveal centralized control.